The turnout is an apparatus that allows the separation of one railroad into two or more, axes of which tangentially meet with the one of the first or form a very small angle therewith.
The simplest case of a turnout is called single or double turnout, which leads to running for taking a way or the other. The main one receives the name of direct railroad and the other one of diverged railroad.
The separation and crossing of both railroad threads are caused by using two elements: the point with tongues and the crossing, which together with the connecting rails between them forms the three main parts of the apparatus:                The point, which consists of two tongue-over-tongue assemblies (semi-points), allowing the splitting of the running threads.        The intermediate or connecting rails, which connect the point to the frog.        The very crossing, which comprises the intercept of the right (left) rail of the direct railroad with the left (right) rail of the diverged railroad.        
The crossing is the part wherein two rails intersect, on the one hand the direct railroad and on the other the diverged railroad.
In order to allow the passage of wheel flanges a discontinuity is inserted into both rails which empty space, is so-called diamond gap.
The extension existing in the rails for allowing the support of the wheel rolling on the outer edge of the rim when the tongue passes through the diamond gap is so-called wing rails. Such crossings are so-called crossings with fixed frog points.
In the transit of vehicle axles through the crossing the wheel shock can be caused on crossing areas. These shocks reduce the life time of both the very turnout and the movable material moving thereon, leading to noises and violent movements affecting the comfort of the passengers.
The bumps have two major consequences:                Produce noises that annoy the neighbors if they are urban roads.        Produce bumps, that annoy the passengers and also produce wears in the very crossing and in the train wheels too.        
In order to ensure the safe passage of vehicles through the crossing (without noises or bumps), it is necessary to eliminate diamond gaps. For removing thereof, the crossing with movable frog points is developed.
In these apparatuses, the frog point is mobile and moves from one position to another, depending from where the train comes, thus eliminating the diamond gaps.
As the frog point is a movable rail, a mechanical drive that makes it moves is needed. Locks are used to ensure that once moved, it will be maintained in that position withstanding the running passes.
This premise is very important because if the frog point is moved, the running pass of the trains would cause their derailment.